1. Field of the Invention
Embodiments of this invention relate generally to electrical circuits and input/output (“I/O”) interfaces, and, more particularly, to a method and driver circuit for controlling slew rates and power of current-mode logic (“CML”) output drivers.
2. Description of Related Art
Electrical circuits and data storage devices have evolved becoming faster and transmitting greater amounts of data. With the increased speed and bandwidth capabilities of electrical circuits and data storage devices, I/O interfaces must be adapted to be compatible with new system requirements. As technologies for electrical circuits and data storage devices have progressed, there has developed a need for backward-compatibility with older and slower technologies, particularly in the area of I/O interfaces. However, power and signal speed considerations introduce substantial barriers to backward-compatibility for I/O interfaces. Parameters such as output voltage, skew and slew rate requirements are particularly problematic.
Typically, in modern implementations for I/O interfaces, either a voltage-mode differential pre-driver or a current-mode differential pre-driver drives a current-mode differential output driver. However, using either of these pre-drivers fails to provide a sufficient solution for backward-compatibility of I/O interfaces. State of the art voltage-mode pre-drivers have limited ranges for tuning slew rates and cannot simultaneously meet multiple, strict skew and slew rate requirements. State of the art current-mode pre-drivers are also incapable of successfully meeting multiple power requirements in conjunction with the necessary slew and skew considerations.